Device and process for the precision measurement of the length of thread wound onto a bobbin

ABSTRACT

Process for measuring the length of the yarn wound onto a bobbin which, at discreet intervals, determines the length of yarn wound in a tangential direction, the length of yarn wound in an axial direction, combining them to obtain the precise partial length wound spirally onto the bobbin at each interval and integrating the partial lengths progressively indicated during the advancement of the bobbin to obtain the overall length.

The present invention relates to a device and process for the precisionmeasurement of the length of the thread wound onto a bobbin in anautomatic bobbin-winder. The invention is described herein withreference to the winding of the thread onto the conical tube forming aconical bobbin, moved with a driving roll having a straight cylindricalshape, but with the notification that it can also be applied in theformation of straight cylindrical bobbins, moved in rotation on conicalrolls.

Bobbin-winders generally consist of a series of heads or winding unitsaligned along the front of the machine and equipped with common servicedevices for their management; they are all independent of each other andconsequently the bobbins in formation can have different advance degreesin their winding. With reference to the scheme of FIG. 1, which brieflyillustrates the collecting section of the wound thread, the bobbin 10 isheld by the bobbin-holder arm 11 equipped with two dead centres 12, 13which are engaged with the conical tube 14 at the base of the bobbin.The conical bobbin in formation 10 rests on its driving roll orcollecting cylinder 16, driven by a motor M. Said collecting cylinder isequipped with traversing throats 17 which distribute the thread 18 withan axial backward and forward movement on the surface of the bobbin 10,whereas the rotating cylinder transmits the torque necessary for itswinding. The number of traversing helixes situated on the drivingcylinder 16 of the bobbin varies according to the yarn counts anddensity of the bobbin to be obtained; the driving cylinder generally has1.5-2-2.5-3 helixes for each turn. The pitch of the helix can beconstant or variable.

The bobbin 10 in formation progressively increases in dimension andweight. The resting pressure of the bobbin on its collection cylinder 16has a great influence on the density of the bobbin itself. In FIG. 1,the bobbin 10 is shown already close to its final dimension.

The length of thread wound onto each of the bobbins, has a real valuewhich significantly varies between the winding units which form thebobbin-winder. It mainly depends on the slippages between the surface ofthe bobbin 10 and the surface of the roll 16 pulling it. There are manyreasons for these slippages. Firstly, there is a geometrical reason dueto the conicity of the bobbin 10 which rests on the straight driving orcollection cylinder 16. In a single axial coordinate of the resting lineof the bobbin on its cylinder, there is a “neutral” point, in which thesurface of the bobbin has the same linear (or tangential) rate as thesurface of the cylinder. In the other points of the resting line of thebobbin there is slippage: towards the tip, the tangential rate is lower,towards the base, the tangential rate is higher in relation to thelesser or greater diameter. The return rate of the threadcorrespondingly has a pulsating trend. The axial coordinate of the“neutral” point is not constant during the whole winding period of thebobbin, said axial coordinate can vary in both a controlled manner forthe modulation of the rate of the bobbin acting on the relative axialdisplacement between the bobbin-holder arm and the driving cylinder, andalso without control.

Cylindrical-bobbins can also have slippages, even if less marked, due tothe variation in the flattening of the bobbin on the cylinder or toparallelism defects between the cylinder and bobbin, as well asconstruction imperfections or in the position between the parts, ormaintenance faults. Variations in the friction coefficient between thevarious bobbin-winding units can occur due to variations in temperatureor humidity, paraffining of the thread, variations in the flow of thebearings of the dead centres due to fouling or lubrication defects. Allof these factors cause slippage between the various winding unitsresulting in differences in length between the bobbins contemporaneouslyproduced which can reach 2-3%.

In the subsequent use of these bobbins, for example in weaving, variousbobbins are used contemporaneously in the parallel feeding of the samemachine and at the end of the bobbin which is the first to be exhausted,all the bobbins must be discharged and substituted with new bobbins: inindustrial practice, the residual yarn wound onto other non-exhaustedbobbins is lost. Particularly when working with high-quality yarns,these non-exhausted bobbins represent a significant cost whether theresidual yarn be recovered or disposed of.

The average slippage which occurs on a bobbin-winder is in the order of1.5%. In current practice, an average overall correction of thetheoretical length established, is inserted into the control unit of themachine, currently a correction factor K, which should recover theaverage slippage of the bobbins. The corrective effect is obtained asthe average of bobbins reaches the desired length, but there is acertain number of bobbins however, which, as a result of dispersion ofthe slippage causes, have a lesser or greater length than the averagewith a Gaussian-type distribution of the real length of±2%.

In the known art, at the beginning of each operating batch thecorrection factor K is determined as follows. A final length to beobtained MF is set on the control unit of the machine. A certain numberof operating winding units are activated: it is even more preferable ifthe whole machine is activated. It is initially assumed that each bobbinis pulled by its cylinder without slippage. For each winding unit N_(c)revs of the activating cylinder 16 are measured, the diameter of thecylinder being known, for each revolution of the cylinder the lengthM_(c) of thread wound is known. In each bobbin-winding unit, thebobbin-winding is terminated when the value of the product N_(c) M_(c)is equal to MF. When the bobbins are finished, they are weighed orunwound and measured, comparing the effective final length value withthe theoretical value MF established. Their ratio corresponds to thecorrection factor K to be introduced into the control unit of themachine to correct the MF for the subsequent bobbins. If the theoreticalvalue established MF, for example, is 1 kg of yarn per bobbin and theactual average value measured on the sample bobbins is 0.984 kg, thecorrection factor K will be equal to 1/0.984.

The operation is then set for the whole bobbin-winder by inserting thefinal theoretical length data MF for each bobbin corrected with thecorrection factor K revealed. On the subsequent production, thecorrection factor K is sample controlled, possibly adjusting it andre-establishing it on the control unit. The correction factors K arerevealed and catalogued for each different operation for possiblere-use.

This length detection method does not take into account the fact thatthe yarn is spirally wound with an axial length component due to thetraversing movement with which the thread is distributed on the bobbin.

More recently alternative systems have been proposed for determining thelength of the bobbin based on the detection of the winding yarn rate,for example in U.S. Pat. No. 5,652,509. According to this prior art, thesystem is based on a thread sensor, consisting of two readers of thethread characteristics (for example the thread image) positioned at adistance L, precise and relatively small. The space/time correlationbetween the images revealed in sequence by the two readers allows thetransit rate of the thread to be determined, moment by moment, shouldthe yarn have frequent identifiable and significant irregularities.

These systems have difficulties with respect to the preparation andfunctioning both in the presence of pulsating rates, as in the case ofconical bobbins, and also when the thread is regular and compact, i.e.its twisting hides its basic irregularities. If, within the distanceinterval L, the thread has the possibility of rotating around itself,there is a further dispersion of the measurements from winding unit tounit. Sensors of this type are therefore insensitive to slippagesbetween bobbin and cylinder, but have other difficulties relating tocalibration and considerable calculation capacity in short times.

An objective of the present invention is therefore to provide a deviceand process for measuring the length of the yarn wound onto a bobbin,which overcomes the drawbacks of the measuring systems according to theknown art and gives a precise and reliable measurement.

The present invention is described herein with reference to its mainapplication to the formation of conical bobbins, for illustrative andnon-limiting purposes, as the device and process according to thepresent invention can find advantageous applications in the formation ofcylindrical bobbins or on machines different from bobbin-winders.

In its accepted meaning as a measuring process of the length of yarnwound onto a bobbin, the present invention is defined in claim 1. Itspreferred variants or embodiments are defined in the dependent claimsfrom 2 to 9.

In its more general meaning as a measuring device of the length of yarnwound onto a bobbin, the present invention is defined in claim 10. Itspreferred variants or embodiments are defined in the dependent claimsfrom 11 to 14.

The measuring system according to the present invention is based on thefollowing logic. The real rising and winding rate of the yarn,insensitive to both slippage and flattening of the bobbin, is directlyproportional to the number of revs of the bobbin multiplied by theactual diameter of the bobbin with respect to its tangential componentV_(y).V _(y)=ω_(r)φ_(r)/2  (a)wherein ω_(r) indicates the angular rate of the bobbin and φ_(r)indicates the bobbin diameter revealed. According to a preferred variantof the invention, said diameter is revealed in a point which isrelatively distant from the contact line between the bobbin andactivation cylinder so as not to be substantially influenced by thedeformation of the bobbin pressed against said cylinder. According tothe present invention, the transversal component of the rate V_(x) dueto the traversing, is also taken into account during the measuring.V _(x)=ω_(c) T/2πN _(e)  (b)wherein ω_(c) is the angular rate of the cylinder, T is the traversingrun and N_(e) is the number of helixes of the cylinder. The actualresulting rate V is then determined by the composition of the two ratesdetermined as follows:V=[V _(x) ² +V _(y) ²]^(1/2)  (c)

This determination logic of the real winding thread rate is insensitiveto any kind of slippage and cause and supplies much greater precisioninformation than that provided by the systems of the known art.

The measuring process of the length of yarn wound onto a bobbin iseffected with the following steps. The length of yarn wound onto theconical bobbin is measured at discreet winding intervals, and the lengthof yarn m_(fy) measured in a tangential direction and in the interval isaccording to the formula:m_(fy)=ΔN_(r)πφ_(r)  (d)wherein ΔN_(r) is the number of revs of the bobbin in the interval andφ_(r) indicates the bobbin diameter revealed during the same interval.

Contemporaneously, within the same interval the length of thread woundm_(fx) measured in an axial direction, is measured according to theformula:m _(fx) =ΔN _(c) T/N _(e)  (e)wherein ΔN_(c) is the number of revs of the cylinder in the interval, Tis the traversing run and N_(e) is the number of helixes of thecylinder. The total length m_(f) wound within the measurement rangetherefore results from the composition of the two components:m _(f) =[m _(fx) ² +m _(fy) ²]^(1/2)  (f)orm _(f)[(ΔN _(c) T/N _(e))²+(ΔN _(r)πφ_(r))²]^(1/2)  (g)

The overall length of wound thread is therefore measured by integratingthe partial lengths progressively recorded during the advancement of thebobbin. If the measuring intervals are sufficiently small to assume thatthe diameter φ_(r) does not substantially vary during each of theseintervals and that the return rate of the thread is constant, theprogressive length therefore faithfully corresponds to the sum of thelengths m_(f) revealed from the beginning of the bobbin.

Discreet measuring intervals of the length wound can be simply equaltime intervals, for example by effecting a measurement every twoseconds, and then summing the lengths measured. These intervals do notnecessarily have to be the same as each other.

According to a preferred embodiment of the present invention, discreetmeasuring intervals are adopted with reference not to time but to theprogressive number of revs of the activation cylinder from the beginningof the bobbin, for example every hundred revs of the cylinder. In thisway, the partial lengths measured each time are cleared of the effectsof the rotation periods at a variable rate due to interruptions in thethread and subsequent joinings, winding modulations to avoid tangling onthe bobbin, or periods of transitory movement for any reason. Inaddition to this, there is the advantage of the simplification that thefirst of the addends of the expression (g) is a fixed term which doesnot have to be determined each time.

The measurement of the real diameter of the bobbin, according to thepreferred embodiment of the present invention, is effected with adistance sensor 20, for example a reflection laser sensor, assembledintegrally on the bobbin-holder arm 11, as shown in FIG. 2, in a fixedgeometrical position and oriented for measuring the distance between thesurface of the bobbin and the emitter, preferably according to astraight line 22, intersecting the axis of the bobbin 21 and orthogonalthereto, in an axial coordinate having a value a. In this way thedecreasing measurement of the distance from the bobbin also supplies themeasurement of the radius of the growing bobbin, as the geometry of thearm is fixed and the arm moves integrally with the growing bobbin. Thedeformation of the surface of the bobbin in the supporting line on thecylinder does not influence the measurement of the diameter as themeasuring point is suitably situated at a due distance from said line,as illustrated in FIG. 2. The bobbin 10 is shown in the figure in itsdimension in the initial phase of its formation.

In the case of conical bobbins, the axial positioning of the sensor 20determines the axial coordinate in which the measurement of the diameteris effected and influences the value of the measurement of the φrevealed in that coordinate. Said axial coordinate can simply be thecoordinate of the barycentre of the bobbin. The axial coordinate ofdiameter sensor can also be selected differently. Once said axialcoordinate and the conicity of the bobbin are known, it is easy to knowthe diameter in each axial coordinate of the bobbin. With reference tothe diagram of FIG. 3, at a certain advancement degree of the bobbin, bymeasuring the diameter of the bobbin φ_(a) at the axial coordinate a andknowing the conicity α of a bobbin having a height T (equal to thetraversing run), the diameter φ_(tip) of the tip of the bobbin and thediameter φ_(base) of the base of the bobbin prove to beφ_(tip)=φ_(a)−2atangα  (h)φ_(base)=φ_(tip)+2Ttangα  (i)whereas the average diameter of the bobbin φ_(average) proves to be:φ_(average)=(φ_(tip)+φ_(base))/2=φ_(a)+(T−2a)tangα  (l)

Once the geometry of the bobbin is known, the measurement of thediameter of the bobbin corresponding to a certain axial coordinateallows the diameter of the spiral wound in each axial coordinate of itsgeneratrix to be calculated, according to a linear law if the cylinderhas a helix cavity with a constant pitch or according to a law of weightif said helix has a variable pitch.

As described so far, the measuring device of the length of yarn woundonto a bobbin according to the present invention consists of thefollowing components:

a progressive revolution counter 30 for the activation cylinder of thebobbin,

a progressive revolution counter 31 for the bobbin. The above revolutioncounters can be produced with different techniques. The revolutioncounter, for example, can be produced as a disk integral with therotating part—for example with a keyed disk 30 inserted onto the axis ofthe activation cylinder 16 in FIG. 1, or on the bearing of the mandrelof the bobbin-holder arm—having an outer surface with magnetic poles N-Sand a Hall-effect probe suitably positioned for revealing the passage ofsaid rotating poles. With each passage of a N polar expansion (or alsothe opposite S) the sensor generates an electric impulse, transmitted tothe control unit with the line 33. As the number of poles arranged onthe circumference of the magnetic disk is known, it is possible, bycounting the number of impulses, to determine the number of revolutionseffected. If the measurement is repeated at known intervals (regular andirregular), it is thus possible to determine the rotation rate of thedisk and consequently of the cylinder or bobbin. Possible alternativescan be obtained by integrally applying toothed wheels of ferromagneticmaterial to the rotating part, controlled with induction probes, or withwheels with N holes or teeth controlled with an optical blockage fork(emitter+receiver), or a reflecting disk with opaque “notches” in thecircumference controlled with an optical reflection sensor.

a measurer 20 of the diameter of the bobbin 10, preferably firmlypositioned on the bobbin-holder arm. It can be produced with variousprocedures. For the direct measurement of the diameter a reflectionlaser can be used, which calculates the distance between the sensor andthe object by means of the triangulation technique, or a so-called“flight time” laser which measures the time displacement between the rayemitted and that reflected: the greater the distance, the greater thedisplacement/delay will be. Alternatively, as the geometry of thebobbin-holder arm is known, the detection of the geometrical position ofthe arm with respect to the activation cylinder allows the measurementof the diameter of the bobbin to be obtained. Said detection can beeffected, for example, with an angular potentiometer which provides themeasurement of the rising of the bobbin-holder arm with respect to theactivation cylinder: when the geometry of the group is known, thediameter of the bobbin can be determined. Analogously, the measurementof a distance of a point integral with the bobbin-holder arm withrespect to a point integral with the cylinder group, by means of aninduction or magnetic or optical sensor allows the diameter of thebobbin in formation to be obtained.

Reflection laser sensors, which form one of the preferred embodiments ofthe invention, can be easily assembled with precision on thebobbin-holder arm 11, for example with the help of positioningtemplates, whereby it is possible to fall within the tolerancesrequested for the precise measuring of the bobbin diameter with thesetypes of sensors.

With respect to the bobbin length, measuring systems of the known art,the measuring process and device according to the present inventionoffer considerable advantages among which the following are worthy ofmention. The measurement is insensitive to slippages, as a velocitymeasurement is effected directly on the bobbin, and also insensitive tothe slippage variation of the bearings and to environmental factors. Themeasurement is also insensitive to the higher or lower density of thebobbin, as the measurement of the bobbin diameter can be effected in anarea which is not influenced by the flattening of the bobbin. Thereading is independent of the type and count of the yarn, which can besingle, twisted, regular or irregular, smooth or hairy.

The calculation of the length is simple, it does not require a highcalculating capacity or high processing rate. The application of thedevice does not hinder the thread run and is in a protected positionwith respect to impact or contacts, also accidental.

1. A process for the measuring of the length of the yarn wound onto abobbin characterized by the sequence of the following steps, effected atdiscreet measuring intervals of the winding and for each interval:determination of the length of yarn m_(fy) wound in a tangentialdirection, determination of the length of yarn m_(fx) wound in an axialdirection, composition of the two lengths of yarn wound in a tangentialand axial direction to obtain the partial length m_(f) spirally woundonto the bobbin at each interval progressively indicated, integration ofthe partial lengths m_(f) progressively indicated during the formationof the bobbin to obtain the length progressively wound.
 2. The processfor measuring of length of yarn according to claim 1, characterized bythe following steps: determination of the length of yarn m_(fy) wound ina tangential direction, on the basis of the measurement of the number ofrevs of the bobbin ΔN_(r) in the interval and the bobbin diameterrevealed φ_(r) during the same interval, according to the formula:m_(fy)=ΔN_(r)πφ_(r) determination of the length of yarn m_(fx) wound inaxial direction in the same interval on the basis of the measurement ofthe number of revs ΔN_(c) of the cylinder in the interval, according tothe formula:m _(fx) =ΔN _(c) T/N _(e) T being the traversing run and N_(e) is thenumber of helixes of the cylinder, composition of the two tangential andaxial components according to the formula:m _(f)=[(ΔN _(c) T/N _(e))²+(ΔN _(r)πφ_(r))²]^(1/2) integration of thepartial lengths m_(f) progressively indicated during the formation ofthe bobbin.
 3. The process for measuring the length of yarn according toclaim 1, characterized in that the discreet measuring intervals refer tothe progressive number of revs of the activation cylinder from the startof the bobbin.
 4. The process for measuring the length of yarn accordingto claim 2, characterized in that the diameter φ_(r) of the bobbin ismeasured in the axial coordinate of the barycentre of the bobbin.
 5. Theprocess for measuring the length of yarn according to claim 2,characterized in that the measurement of the diameter of the bobbinφ_(r) is effected with a distance sensor, assembled integrally onto thebobbin-holder arm.
 6. The process for measuring the length of yarnaccording to claim 5, characterized in that the measurement of thediameter of the bobbin φ_(r) is effected with a reflection laser sensor.7. The process for measuring the length of yarn according, to claim 5,characterized in that the measurement of the diameter of the bobbinφ_(r) is effected in a point suitably positioned at a due distance fromthe supporting line on the cylinder, so that the deformation of thesurface of the bobbin does not influence the measurement of the diameterof the bobbin.
 8. The process for measuring the length of yarn accordingto claim 2, characterized in that the measurement of the diameter of thebobbin φ_(r) is effected by detecting the geometrical position of thearm itself with respect to the activation cylinder.
 9. The process formeasuring the length of yarn according to claim 8, characterized in thatthe detection of the geometrical position of the arm with respect to theactivation cylinder is effected with an angular potentiometer whichprovides the measurement of the rising of the bobbin-holder arm (11)with respect to the activation cylinder (16).
 10. Device for measuringthe length of the yarn wound onto a bobbin comprising the followingcomponents: a progressive revolution counter (31) for the activationcylinder of the bobbin, a progressive revolution counter (30) for thebobbin, a measurer (20) of the diameter of the bobbin φ_(r).
 11. Thedevice for measuring the length of the yarn wound onto a bobbinaccording to claim 10, characterized in that the revolution counterdevices (30, 31) are produced as magnetic disks integral with therotating part, equipped with N-S magnetic poles associated with aHall-effect probe positioned for revealing the passage of said rotatingpoles.
 12. The device for measuring the length of the yarn wound onto abobbin according to claim 10, characterized in that the measurer (20) ofthe diameter of the bobbin φ_(r) is a distance sensor firmly positionedon the bobbin-holder arm.
 13. The device for measuring the length of theyarn wound onto a bobbin according to claim 12, characterized in thatthe measurer (20) of the diameter of the bobbin φ_(r) is a reflectionlaser sensor.
 14. The device for measuring the length of the yarn woundonto a bobbin according to claim 10, characterized in that the distancemeasurer (20) is suitable for revealing the diameter of the bobbin φ_(r)(10) in a point duly distant from the supporting line on the cylinder(16), so that the deformation of the surface of the bobbin does notinfluence the measurement of the diameter of the bobbin.